Apparatus and method for precooling material by vacuum-induced evaporation



1952 M. w. BEARDSLEY ETAL APPARATUS AND METHOD FOR PRECOOLING MATERIALBY VACUUMJNDUCED EVAPORATION 2 SHEETSSHEET 1 Filed July 18, 1949 IN VENTORS W. BEARDSLEY ETAL M. APPARATUS AND METHOD FOR PRECOOLING MATERIALBY VACUUM-INDUCED EVAPORATION Dec. 16, 1952 Filed July 18, 1949 PatentedDec. 16, 1952 UNITED STATES PATENT OFFICE Melville W. Beardsley, Venice,and RexL. Brunsing,. San Francisco, Calif.

Application July 18, 1949, Serial No. 105,302

16 Claims. 1

This invention relates generally to the precooling of vegetable produceprior to shipment thereof, and more particularly, to a refrigerationsystem for this purpose which cools the produce by reducing the vaporpressure surrounding the same, whereby to cause rapid evaporation of thesurface moisture. These general principles are disclosed in Patent No.2,344,151, issued March 14, 1944, to Morris Kasser.

The method. of cooling disclosed in the above mentioned patent may betermed generally "vacuum cooling, and depends for its operation on theprinciple that evaporating water, or for that matter any liquid, absorbsheat of vaporization from the surrounding media.

One of the principal advantageous uses of the vacuum cooling principleis in the precooling of vegetable produce such, for example, as lettuce,celery, and other leafy vegetables, prior to their shipment inrefrigerator cars. Prior to the use of vacuum cooling, it was thepractice to interlayer the packed produce with layers. ofcrushed ice asthe material was packed, so that the entire body of. the shipment wouldbe kept at a temperature at or near 32 F. Such practice has numerousdisadvantages, among which are the fact that the lumps of crushed icetend to bruise tender vegetables such as lettuce; the water from themelting crushed ice causes a certain degree of deterioration of theproduce and is generally a nuisance in the shipment; and the crushedice, in spite of great care in distributing the same, does not maintainas uniform a temperature throughout the body of the packed shipment asis desired. Still further, the operation of packing the crushed ice intocrates or other containers with the produce is a costly andtime-consuming phase of the shipping operation.

With a view of avoiding the foregoing difiiculties, it has been foundadvantageous to pack the produce without ice, and" place the packedcrates. in a large, hermetically scalable chamber, and thereafterevacuate the chamber, whereupon the moisture on. the leaves of theproduce evaporates and rapidly reduces the temperature of the vegetablematerial. It will be seen that the cooling eiiected in this manner takesplace substantially uniformly throughout the body of the vegetable,rather than merely cooling the surface thereof as is the case with iceor other external refrigeration means; The crated produce thus precooledmay then be packed into refrigerator freight cars and shipped, the onlyrefrigeration. thereafter: required being that pro- 2 vided by the icebunkers in therefrigerator'car itself.

The present invention concerns itself with the eificient, continuousoperation of a multiplechamber vacuum cooling system operating on thegeneral principles above described.

A major object of the invention isto provide a cooling system in whichthe power required to evacuate the cooling chambers is reduced to apractical minimum and in which the optimum use is made of the'potentia lenergy of the evacuated chambers.

Another object of the invention is toprovide a system of the classdescribed in which a number of evacuating pumps are employed, certain ofthe-pumps bein designed specifically for efiicient operation on air, andother pumps being designed to operate most efiiciently in the'pumping ofwater vapor;

Still anotherobiectof the invention is to-'pro'- vide a refrigeratingsystem in which the time periods for loading and unloading the coolingchambers may be so telescoped as to make possible substantiallycontinuous operation of the power plant whereby the same need not beshut down for lengthy periods between successive cooling phases of theoperation.

The foregoing and other objects and advantages of the invention willappear from the following detailed description thereof, as incorporatedin a plant for pre ooling lettuce prior to shipment. Itwill be realizedof course, that the system is not confined inits use to the cool.- ingof lettuce but canbe used with equivalent effect and with little or nomodification on other materials. The description isillustratedin theattached drawings, wherein:

Figure 1 is a semi-schematic elevational view. taken through a dualchamber cooling system embodying the present invention;

Figure 2 is an elevationalsection takenonthe line 2 2 in Figure 1;

Figure 3 is an elevationalmedial section taken through a barometriccondenser system employed in connection with theplant in Figure l; and

.Figure 4 is a time-pressure graph illustrating the cyclic operation ofthe plant illustrated in Figure 1.

The dual chamber cooling system illustrated in Figure l is bilaterallysymmetrical, that is, the elements associated with one of the coolingchambers are, for the large part, duplicated in connection with theother chamber. Accordingly, it is necessary herein: to" describeindetailonly character l8 in Figure 1. in the conduits 16 so as to close thelatter at cerone set of elements, it being understood that unlessotherwise noted, such elements are duplicated in connection with theother chamber. The chambers have been designated generally by thereference character It! and differentiated between themselves by thereference characters A and B, as shown in Figure 1.

Each of the chambers comprises a generally cylindrical hermeticenclosure provided with an air-tight door (not shown) whereby packedcrates of produce 1 I may be wheeled into and out of the chamber onconventional wheeled cnveyors l2. Each of the chambers is provided withtwo exhaust conduits l5 and it, the conduit l5 being for connection to afirst pump adapted to the purpose of initially exhausting substantiallyall of the air from the chambers l0, and the conduit 16 being forconnection to a second pump adapted to the purpose of further reducingthe vapor pressure in the chambers l 0 after substantially all of theair has been exhausted therefrom.

The exhaust conduits l5 are interconnected by a manifold I9 in which aremounted two or more steam ejector pumps 2! each of which comprises arestrictive throat or venturi portion 22 into which a nozzle 23 directsa jet of steam provided through a manifold connection 24 under thecontrol of a valve 25. The air ejector pumps 22 exhaust upwardly throughsuitable exhaust pipes 26, discharging the steam and air carried thereby preferably through the roof of the building in which the coolingsystem is housed. The air ejector pumps 22 are especially designed tohandle air at a pressure ratio up to approximately to 1, that is, thepumps will continue to operate, exhausting against atmospheric pressureuntil the pressure within the chambers 10 reaches approximately threeinches of mercury. After the chamber has been evacuated to thispressure, the air pumps 22 cease to operate efliciently, and in factwill cease to operate altogether, discharging the steam from the nozzle23 back into the chamber Ill. Accordingly, suitable valves 29 areprovided in the exhaust connection l5 whereby to close the conduit of aparticular chamber It when the pressure therein approaches that at whichthe air pump 22 will no longer operate efilciently. Suitablepressure-operated controls may be connected to the valve 20 for thispurpose, and such controls being of well known design and operation neednot be described in detail herein.

At certain stages of the cooling operations, as will hereinafter appear,it is desired to bleed one chamber Ill into the other, and for thispurpose an interconnecting pipe 35 is provided, having a control valve36 therein.

.As the air pressure in the chamber H3 is reduced by the operation ofthe pumps, the rate of evaporation of the moisture on the surface of theproduce increases and becomes very rapid when the pressure is reduced tothe point where water boils at the then ambient temperature. At thisstage in the operations the contents of the chamber I!) arepredominantly water vapor. .In order to reduce the temperature of theproduce in the crates H to that approaching freezing, it is necessary toreduce the vapor pressure in the chamber in considerably below thethree-inch limit which can be eiiected by the air pumps 22. To this end,a second pump (herein termed a vapor pump) is provided andinterconnected to the two chambers I0 by the conduits 15, the vapor pumpbeing indicated by the reference Valves IT are provided tain points inthe cooling cycle as will be hereinafter described.

The vapor pump 18 is similar in general design to the air pumps 22,although the shape of the throat 36 of the vapor pump 18 and the numberand dispositions of the nozzles 3! thereof are specifically designed tooperate on a gaseous mixture comprising principally water vapor, ratherthan the substantially pure air for which the air pumps 22 are designed.The design of gas ejector pumps for specific gases is well known in theart and the details of such design forming no part of the presentinvention, are not set forth herein.

The maximum pressure ratio of the vapor pump l8 being substantially thesame as the air pumps 22, i. e., 10 to 1, it is necessary if the vaporpump i8 is to operate efficiently that it exhaust against a pressuresubstantially reduced from atmospheric. To this end, the exhaust of thevapor pump it! is directed through a vertical conduit 33 into abarometric condenser 66, details of which are illustrated in Figure 3.

The condenser 49 will be seen to comprise a generally cylindrical body4|, closed at its upper and lower ends, and having a Water inletconnection 12 adjacent the upper end thereof. The water from the inletconnection 42 discharges into an annular basin formed by a circularweirlike member 43, having a notched upper edge whereby the waterdischarges inwardly from the annular basin surrounding the weir 43 in anumber of small streams around the axis of the condenser body 4i. As thewater descends through the condenser 4%, it falls on tray-like bafiles44 having upturned edges over which, in turn, the Water falls in a sheetdownwardly onto the next baffle. The cooling water and condensate isdischarged through a standpipe 45 at the bottom of the condenser body M.

The steam and vapor from the pump I8, directed through the conduit 33,enters the condenser adjacent the lower end thereof as shown in Figure3. Thus, as vapor passes upwardly through the condenser 45, it is passedin intimate heat-transfer relation with the water therein, causingcondensation of a substantial proportion of the water vapor. Such vaporas is not condensed in the condenser 4% passes out of the top thereofthrough a conduit 46 to the intake of a second stage vapor-air pump 41,which in turn discharges into a second stage barometric condenser 69,which in turn is exhausted by a third stage pump 5|, which exhausts toatmosphere. The principal function of the final stage pump 5| is toremove from the system such residual air as has not been removed by thepumps 22, and such air as may leak into the system during the coolingcycle.

Each of the barometric condensers 4| and 49 is provided with a standpipe45 and 52 respectively, the lower ends of which are immersed in a tank53 having a discharge 54. The purpose of the tank 53 is to provide a.trap at the lower ends of the standpipes. It will be realized of coursethat as the pressure in the condensers 40 and 49 is reduced, the waterrises in the standpipes 45 and 52. These pipes are somewhat greater than34 feet in height so that the theoretical lower limit of pressureattainable in the condensers is equal to the vapor pressure of water atthe ambient temperature.

The second stage condenser 49 is provided with a water intake 55,equivalent to that of the first duit- 35 under the control of the valve36 stage-.- condenserr' 40., and: the. internal. constructionrofthetcondenseriflt is'snbstantially: thev same as thatr of the primary:stage: condenser: 40;. exceptfonzacsmalleri scale; The. pressure inthecondenser: 40.1 being-xgreatlyi depressed, the; operationotthezvaporipmnpt t8 downitcr pressures less than one inch. ofmercuryin. the chamber" lllis possible:.

Thea steam for the operation. of the second and third stagespumps is:provided" through a connection. fillrhaving. a; branch: connection 48leading to the second'sta'gepump 41; Alllsteanr foroporation oithesystem'iszprovided bya single con-- ventional steam plant: (notshown)...

Each: of. the. chambers ll); is; provided, with. avapor'inta'keconnectiorr. 6B andza control valve .6 whereby" small.amounts-mi: water vapor may be admitted to. thevchamberr under certainconditions near the end of the; cooling: cycle: The vapor admitted inthis. manner serves to" level of the cooling process whereby to preventinadvertent freezing of the outside oi vegetables, such for example,ashea'ds of lettuce; before the internal temperature of the lettuce: hasbeen reduced to the: desired point. Usually the vapor intake connectionBil'is not employed except for limited'operationswhen only one of thechamhers m is inoperatio-n.

In the normal cyclic operation of the dual chamber cooling system,illustrated. in Figure l, the produce is alternately loaded into the twochambers, each of which is then successively evacuated of air andthereafter of' vapor. One efiicaciousoperation cycle is illustrated inFigure 4', wherein it will be seen that, at certain points in theoperation, the two chambers are interconnected as through" theinterconnecting con- As indicated in the l'egend of Figure 4, thepressure in chamber A is indicated by a. dashed line, whereas thepressure inchamber 3 is indicated in f'ullline; It'-w-ill be noted that;at the point in thecycl'e where-the two chambers are interconnected, thedescending pressure curve of the particular chamber then being cooled(evacuated is relatively flat, thus indicating that a considerableamount of time would be taken to reach the desired pressure if pressurereduction continued at the then rate; It will be noted,

however, that interconnection with the other chamber causes a materialsteepening of curve at-this point, and thus makes use Of thepotential"energy of the vacuum in the chamber in which" the cooling has beencompleted to effect pressure-reduction in-theother cooling chamber. Whenthe'pres'surei'n the two'chambers is equalized as is indicated in Figure4 by the crossin of the two curves, the valve 36 and one of the valvesIT are-closed so as topermit further reduction of vapor pressure in thethen cooling chamber.

Another important advantage of the present system is achieved bythe'iact that two separate pumping systems are provided, onespecifically designed for evacuating the air andthe other for evacuatingvapor. It will be realized that if only the vapor pump- H! wereprovided, the system could operatebut that the rate at which air couldbe evacuated from either of thechambers It: would be limited to thecapacity ofthe final stage pump 5l- Thus, a system which comprised onlythe vapor pump I 8 and the condenser system illustrated in Figure 3would require a considerable period of time toexhaust theair fromthechamber prior tothe portion of the cycle which. reduces: the water vaporpress'ure. This substantial amount ofti'me could-be avoided, of'course,by employing a large capacity air-pump in place of the relatively smallcapacity pump 51 used in the present system, but a system employing alarge air pump continuously throughout: the cycle would require aninordinately large amount of steam during the portion of the cycleinwhich: substantially pure vapor is being exhausted from the chamber.Thus, the present system in which two diiferent sizes and designs ofpump are employed successively in evacuating the chambers is much moreefficient than a singlepump system.

It will be realized, of course, that thenumber of chambers employed maybe multiplied beyond the twoillustrated herein to further increase theeffi'ciency of the pumping system. The increase of efficiency is due. inpart to the fact that the demands on the steam plant is relativelyconstant, the load being shifted successively from one chamber to theother, thus to obviate intermediate shutdown periods when no steam isrequired. Such intermittent demand systems are inefficient because ofthe necessity of periodically reducing the boiler fire or,alternatively, providing for storage of substantial quantities of steamunder relatively high pressures.

While the system and method illustrated and described herein is fullycapable of achieving the objects and providing the advantageshereinbetore stated, it will berealized that considerable modificationis possible without departing from the spirit of the invention. For thisreason, We do not mean to be limited to the form shown and described,but rather to the scope of the appended claims.

we claim:

1. In a vacuum refrigeration system of the class described: a pluralityof enclosed chambers each having an opening whereby produce may beloaded into said chamber and a hermetically scalable closure for saidopening; a steam ejector air pump having a plurality of intake conduits,one connected to each of said chambers and an exhaust to atmosphere; asecond steam ejector pump having a Venturi throat designed and adaptedto pump Water vapor and exhaust the same into a condenser, said ejectorpump having a plurality of intake conduits, one connected to each ofsaid chambers; a condenser having a condensation chamber connected toreceive the discharge from said ejector pump, cooling water intake meansfor said condensation chamber, cool.-

' ing water and condensate discharge means, and

means to reduce the total pressure in said condensation chamber; andvalves in said. intake conduits to selectively close the same whereby tosequentially connect said air pump and said ejector pump to saidchambers to first evacuate a substantial proportion. of air from a givenchamber and thereafter reduce the pressure of vapor in said givenchamber evaporated from produce therein.

"- take conduit connected to said chamber whereby .to exhaust air fromthe same; a second steam ejector pump having a Venturi throat with a.steam nozzle aligned therewith, designed and arranged to pump watervapor and exhaust the same into a condenser, said second pump having anintake conduit connected to said chamber; a condenser having acondensation chamber connected to receive the discharge from said secondpump, cooling water intake means and cooling water and condensatedischarge means for said condensation chamber; a second stage steamejector vapor-air pump having its intake connected to said condensationchamber whereby to reduce the total pressure therein; and valves in saidfirst intake conduits whereby to effect sequential operation of saidfirst and second pump to first evacuate a substantial proportion of airfrom said chamber and thereafter reduce the pressure of vapor evaporatedfrom produce in said chamber.

3. In a vacuum refrigeration system of the class described: a pluralityof enclosed chambers each having an opening through which produce may beloaded into said chamber, and a hermetically sealable closure for saidopening; an air pump having a plurality of intake conduits, oneconnected to each of said chambers; an ejector pump having a venturi andsteam nozzle therein designed and arranged to pump water vapor andexhaust the same into a condenser, said ejector pump having a pluralityof intake conduits, one connected to each of said chambers; a condenserhaving a condensation chamber connected to receive the discharge fromsaid second pump, cooling water intake means and cooling water andcondensate discharge means for said condensation chamber; a second stagesteam ejector vapor-air pump having its intake connected to saidcondensation chamber whereby to reduce the total pressure therein;valves in said first intake conduits whereby to effect sequentialoperation of said first and second pump to first evacuate a substantialproportion of air from said chamber and thereafter reduce the pressureof vapor evaporated from said produce in said chamber; and a conduithaving a control valve therein connected between said chambers wherebyselectively to bleed one of said chambers into the other to equalize thepressures therein.

4. In a vacuum refrigeration system of the class described: a pluralityof enclosed chambers, each hermetically constructed and adapted towithstand external pressure, and each having an opening through whichproduce may be loaded into said chamber and a hermetically sealableclosure for said opening; first and second manifolds eachinterconnecting said chambers; a bleed conduit interconnecting saidchambers; a first steam ejector pump having a venturi throat, designedand arranged to pump air and exhaust the same in-to atmosphere, saidfirst pump having its intake connected to said first manifold; a secondsteam ejector pump having a Venturi throat, designed and arranged topump water vapor and exhaust the same into a condenser, said second pumphaving its intake connected to said second manifold; a condenser havinga condensation chamber connected to receive the discharge from saidsecond pump, cooling water intake means for said condensation chamber,and cooling water and condensate discharge means; a second stage steamejector pump having its intake connected to receive vapor from saidcondensation chamber and designed and adapted to exhaust into a secondcondensation chamber; a second condensation chamber connected to receivethe exhaust from said second stage pump and having cooling water intakemeans, and cooling water and condensate discharge means; a third stagepump having its intake connected to receive vapor from said secondcondensation chamber, said third stage pump being designed and arrangedto discharge into atmosphere; control means including a plurality ofvalves in said first conduit, one positioned between said first pump andeach of said chambers, a plurality of valves in said second manifold,positioned between said second pump and each of said chambers, and avalve in said bleed conduit whereby to effect sequential operation ofsaid pumps to first evacuate a substantial proportion of air from agiven chamber, thereafter reduce the pressure of vapor in said givenchamber, and thereafter equalize the pressures in said chambers.

5. The method of precooling vegetable produce which comprises the stepsof: placing a portion of said produce in a first hermetically sealedenclosure; placing a second portion of said produce in a secondhermetically sealed enclosure; evacuating a substantial proportion ofthe air in said first enclosure; thereafter reducing the vapor pressureof vapor in said first enclosure; evacuating a substantial proportion ofthe air from said second enclosure concurrently with said reduction ofvapor pressure in said first enclosure; thereafter interconnecting saidenclosures whereby to further reduce the pressure in said secondenclosure while permitting an increase of pressure in said firstenclosure; disconnecting said enclosures from each other when thepressures therein are equalized; thereafter continuing to reduce thevapor pressure in said second enclosure; and admitting air into saidfirst enclosure concurrently with said last-mentioned reduction ofpressure in said second enclosure.

6. A vacuum refrigeration system comprising: a pair of hermetic chambershaving air-tight doors to receive material for cooling in said chambers;a first, a second, and a third conduit, each interconnected between saidchambers; an air pump connected intermediate the ends of said firstconduit and arranged to exhaust air therefrom and discharge intoatmosphere; 2. pair of valves in said first conduit, one between each ofsaid chambers and said air pump; vapor exhausting means including asteam ejector pump connected in said second conduit and arranged toexhaust vapor therefrom, and a condenser connected to receive thedischarge from said ejector pump; a pair Of valves in said secondconduit, one between each of said chambers and said ejector pump; and avalve in said third conduit operable independently of said first andsecond conduit valves to bleed one of said chambers into the other.

7. A vacuum refrigeration system comprising: a pair of hermetic chambershaving air-tight doors to receive material for cooling in said chambers;a conduit system having a plurality of passageways interconnectedbetween said chambers; an air pump connected to said conduit system toexhaust air therefrom and discharge the same to atmosphere; first valvemeans in said conduit system to communicate said air pump selectivelywith one or the other of said chambers; vapor exhausting means includinga second pump connected to said conduit system to exhaust vaportherefrom; second valve means in said conduit system operableindependently of said first valve means to communicate said second pumpseleca ists ti vely with one or the other off said chambers; acommonpower source connected ,to bothsaid pumps to operate the same; andthird valve means in said conduit system operable independently ofsaidfirst and second valvemeans selectively to interc'ommunicate or separatesaid chambers.

8. .A vacuum refrigeration system comprising: a pair of hermeticchambers having air-tight doors to receive material for cooling in saidchambers; a conduit system having a plurality of passagewaysinterconnected between said chambers; an air pump connected to saidconduit system to exhaust air therefrom and discharge the same toatmosphere; a first pair of Valves in said conduit system, one betweeneach'of said chambers and said air pump; vapor exhausting meansincluding a steam ejector pump connected in said conduit system andarranged to exhaust vapor therefrom and a condenser connected to receivethe discharge from said ejector pump; a second pair of valves insaidconduit system, one between eachof said chambers and said ejector pump;and-a third Valve in said conduit system operable independently of saidfirst and second valve pairsto bleed one of said chambersinto the other.

9. A vacuum refrigeration system comprising: a pair of hermetic chambershaving air-tight doors to receive material for cooling in said chambers;a first, a second, and a third conduit interconnected between saidchambers; an air pump connected intermediate the ends of said firstconduit and arranged to exhaust air therefrom and discharge intoatmosphere; a pair of valves in said first conduit, one between each ofsaid chambers and said air pump; vapor exhausting means including asecond pump connected in said second conduit and arranged to exhaustvapor therefrom; a pair of valves in said second conduit, one betweeneach of said chambers and said second pump; a common power sourceconnected to both of said pumps to operate the same; and a valve in saidthird conduit operable independently of said first and second conduitvalves to bleed one of said chambers into the other.

10. A vacuum refrigeration system comprising: a pair of hermeticchambers having air-tight doors to receive material for cooling in saidchambers; a first, a second, and a third conduit interconnected betweensaid chambers; an air pump connected intermediate the ends of said firstconduit and arranged to exhaust air therefrom and discharge intoatmosphere; valve means in said first conduit to selectively block offone or the other of said chambers from said air pump; vapor exhaustingmeans including a steam ejector pump connected in said second conduitand arranged to exhaust vapor therefrom, and a condenser connected toreceive the discharge from said ejector pump; valve means in said secondconduit arranged to selectively block off one or the other of saidchambers from said steam ejector pump; and a valve in said third conduitoperable independently of said first and second conduit valve means tobleed one of said chambers into the other.

11. A vacuum refrigeration system comprising: a pair of hermeticchambers having air-tight doors to receive material for cooling in saidchambers; a first, a second, and a third conduit interconnected betweensaid chambers; an air pump connected intermediate the ends of said firstconduit and arranged to exhaust air therefrom and discharge intoatmosphere; valve means in said first conduit to selectively block offone or the other of said -chan'ribersfromsaid air pump; vapor exhaustingmeans including .a second pump connected in said second conduit andarranged toexhaust vapor therefrom, a common power source connected toboth of said pumps to operate .thesame; valve meansin said secondconduit arranged to selectively block off one or the other of saidchambers fromsaidisecond pump; and a valve in said third conduitoperable i'ndependently of said first and second conduit valves tobl'eedone of said chambers into the other.

12. A vacuum refrigeration system comprising; a pair of hermeticchambers having air-tight doors to receive material .for cooling in saidchambers; a first, a.second,.-and a third conduit each interconnectedbetween said chambers; -a steam powered air pump connected intermediatethe ends of said first conduit and. arranged to exhaustair therefrom anddischargeinto atmosphere'; valve means in'said first conduit arranged toselectively block off one or the otherof said chambers from said airpump; steam powered vapor exhausting means connected in said-secondconduit and arranged .to exhaust vapor therefrom; valve means in saidsecond conduit arranged to selectively block on one or the other of saidchambers from said vapor exhausting means; and a valve in said thirdconduit operable independently of said first and second conduit valvemeans to bleed one of said chambers into the other.

13. In a vacuum refrigeration system of the class described: an enclosedchamber of hermetic construction adapted to withstand external pressure,said chamber having an opening through which produce may be loaded intosaid chamber and a hermetically scalable closure for said opening; asteam ejector pump having a Venturi throat with a steam nozzle alignedtherewith, designed and arranged to pump air and exhaust the same intoatmosphere, said pump having an intake conduit connected to said chamberwhereby to exhaust air from the same; vapor removing means including asecond steam ejector pump connected by an intake conduit to saidchamber; a condenser to receive the discharge of said second pump, andmeans to reduce the total pressure in said condenser; and valves in saidpump intake conduits to effect sequential operation of said first andsecond pumps to first evacuate a substantial proportion of air from saidchamber and thereafter reduce the pressure of vapor evaporated fromproduce in said chamber.

14. In a vacuum refrigeration system of the class described: an enclosedchamber of hermetic construction adapted to withstand external pressure,said chamber having an opening through which produce may be loaded intosaid chamber and a hermetically sealable closure for said opening; asteam powered air pump arranged to exhaust into atmosphere, said pumphaving an intake conduit connected to said chamber whereby to exhaustair from the same into atmosphere; vapor removing means including asecond steam powered vapor pump connected by an intake conduit to saidchamber, a condenser to receive the discharge of said second pump, andmeans to reduce the total pressure in said condenser; and valves in saidpump intake conduits to effect sequential operation of said first andsecond pumps to first evacuate a substantial proportion of air from saidchamber and thereafter reduce the pressure of vapor evaporated fromproduce in said chamber.

15. The method of continuously cooling moist" produce which comprisesthe steps of: loading successive batches of produce alternately into oneor the other of two hermetically sealed enclosures, and after eachloading closing and subjecting the loaded enclosure to repetitivecycles, each consisting of the sequential steps of evacuating asubstantial proportion of air therefrom, reducing the vapor pressuretherein to a predetermined value, connecting said enclosure to the otherenclosure, disconnecting said enclosure from said other enclosure,admitting air to said enclosure, and opening and unloading the same;said cycles being performed in such alternate time phase relationshipthat one of said enclosures is at said air evacuation stage and theother is at said reduced vapor pressure when said enclosures areconnected together, whereby to bleed the former enclosure into thelatter.

16. The method of continuously cooling moist produce which comprises thesteps of loading successive batches of produce alternately into one orthe other of two hermetically sealed enclosures, and after each loadingclosing and subjecting the loaded enclosure to repetitive cycles, eachconsisting of the sequential steps of evacuating a substantialproportion of air and vapor therefrom, to reduce the vapor pressuretherein to a predetermined value, connecting said enclosure to the otherenclosure, disconnecting said enclosure from said other enclosure,admitting air to said enclosure, and opening and unloading the same;said cycles being performed in such alternate time phase relationshipthat one of said enclosures is at said reduced vapor pressure and theother enclosure is loaded closed and at a pressure substantially greaterthan said value when said enclosures are connected together, whereby tobleed the latter enclosure into the former.

MELVILLE W. BEARDSLEY.

REX L. BRUNSING.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,256,954 Smith Sept. 23, 19412,344,151 Kasser Mar. 14, 1944 2,345,548 Flosdorf Mar. 28, 19442,436,693 Hickman Feb. 24, 1948

